Sonochemical Synthesis of Fe-Doped Bi4MoO9 for Efficient Photo-, Piezo-, and Photopiezocatalytic Applications

In this work, pure and iron-doped (1, 2, and 4 mol.%) Bi 4 MoO 9 nanoparticles were successfully synthesized via a sonochemical method, proving to be a rapid and energy-efficient route. The samples were characterized in terms of crystal structure, morphology, and optical and electrochemical properties using x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–Vis spectroscopy, electrochemical impedance spectroscopy (EIS), and Mott–Schottky analysis. Results demonstrated that Fe-doping reduced crystallinity and average crystallite size (from 26.3 nm to 4.9 nm), modifying particle morphology and increasing the specific surface area by up to 7-fold. Furthermore, iron incorporation tuned the material’s bandgap from 2.94 eV to 2.41 eV for the 4%-doped sample and enhanced the separation and mobility of charge carriers ( e − / h + ). In methylene blue dye degradation assays, the 4% Fe-doped sample (BMO4F) exhibited superior performance across all modalities, achieving 88% degradation via photocatalysis and 100% via piezocatalysis. Notably, an exceptional synergistic effect was observed in the photopiezocatalytic process, where the coupling of light excitation with ultrasound-induced polarization resulted in the total mineralization of the pollutant in just 45 min. This process exhibited a kinetic rate constant 5 times higher than that of photocatalysis alone, highlighting the system’s innovative potential for wastewater treatment.